router problem?

I'm using Windows XP, fully updated. For a while I've been unable to connect
my laptop wirelessly to my network (I have a wireless router). However, it
works when plugged in to the router. I recently discovered that my netbook,
which appeared to connect wirelessly, was actually using someone else's
unsecured network. My local ISP suggested that I unplug the modem, unplug
the router, wait 30 seconds, plug in the modem, and then, after the DSL
light came on, plug in the router. I did all that, but the situation remains
the same.

Any suggestions?

Thank you!

Jo-Anne